Question: Judy built a rectangular patio that is $9$ meters wide and has a perimeter of $40$ meters. What is the length of Judy's patio?
Solution: Perimeter is the distance around a closed figure. We can find the perimeter of a shape by adding all the side lengths. The perimeter is $40}\text{ m}$ and the width is ${9}\text{ m}$. $\text{Perimeter}= 40\text{ meters}\,$ $\,9\text{ m}$ $\,9\text{ m}$ $\begin{aligned} P} &= {l} + {w} + {l} + {w}\\\\ 40} &= {\ell} + 9 + {\ell} + 9 \\\\ 40} &= {\ell} + {\ell} + {18}\\\\ 22 &= {\ell} + {\ell} \end{aligned}$ What number can we add twice to get $22$ ? The length of the patio is ${11}$ meters.